True wisdom is less presuming than folly. The wise man doubteth often, and changeth his mind; the fool is obstinate, and doubteth not; he knoweth all things but his own ignorance.
Do your duty in all things. You cannot do more, you should never wish to do less.
For me, something will come in my head and I'll either end up calling my cell phone to record it, or I'll just pick my guitar up and see what comes out. Sometimes it sucks, sometimes it doesn't. So there's really no set method behind it.